It’s impossible to say for certain, but language experts think Julius Caesar first offered the quote “Divide et impera,” which is Latin for “Divide and Conquer.” While Caesar was referring to city states, whole countries, in the garden we’re talking about your perennials, those plants that stand faithfully year after year. There are a number of varieties of perennials that do better when they’re thinned. They’re not the colorful plants you have to plant new each year, those are called annuals.
Fall is a great time to get out and look at your perennials, studying your garden for overgrown bunches or clumps browning in the middle. If you find crowding and bunching, it’s time to call in the centurions and divide and conquer. The result will be healthier plants and savings on landscaping since what you already have and what is already doing well can be spread around. An added bonus is the chance to can up divided plants and give them as gifts to your friends.
Here are some answers from California Master Gardeners and local nurseries on how to divide your perennials:
When should perennials be divided? About every three to five years. However, some, like columbines, poppies and euphorbias, shouldn’t ever be divided, even if they start to clump. Woody perennials like lavender, rosemary or the artemisias (diverse plant genus with between 200 to 400 species belonging to the daisy family) also don’t divide well.
When is the best time to transplant? Fall is best because the ground has cooled, but it’s not yet turned wintry cold. It also provides cloudier, cooler days, which helps minimize transplant shock and get your new divisions off to a good start.
What should be done to prepare for transplant? If your yard hasn’t already had a good, soaking rain, thoroughly water all plants to be divided a day or so before you dig in. Also, dig planting holes for the new divisions, filling with water and allowing to fully drain. That prevents transplants from drying out. You can also pot up divisions and let them grow bigger before transplanting in the spring. Make sure your tools are clean, and equally important, very sharp.
How should the section be lifted from the main plant? Use a sharp, pointed shovel or spading fork to dig down deep on all four sides of the section, several inches from the main plant. Pry underneath to get the roots and lift the whole clump to be divided. If the plant is very large and heavy, section it right in the ground with a sharp shovel before removing. Shake or hose off loose soil and remove dead leaves and stems. Loosen tangled root balls with your fingers, gently combing out tangles.
Depending on the root system, divide your plants as follows:
- Plants with spreading root systems, that have just a mess of disorganized roots, include asters, bee balm, lamb’s ear, purple cornflowers and many other common perennials. They can be pulled apart by hand, or cut apart with shears or a sharp knife. Divide the outer ring of the plant into clumps of three to five vigorous shoots with roots attached.
- Plants with clumping root systems start from a central clump with multiple growing points and usually have thick, fleshy roots. This group includes astilbes, hostas, daylilies and many ornamental grasses. A sharp knife is handy with these soldiers, as it is often necessary to cut through the thick crowns to separate the divisions. You can also pry apart these roots with two digging forks held back to back. Make sure at least one developing eye or bud exists on each division.
- Rhizomes are stems that grow horizontally at or above the soil level. Irises are the most common perennial with this type of root system. Divide irises any time between a month after flowering until early fall. (Time is running out for this perennial) Cut and discard rhizome sections that are one year or older and/or showing signs of disease or insect damage. Iris divisions should retain a few inches of rhizome and one fan of leaves, trimmed back halfway. Replant with the “shoulders” of the rhizome showing above soil level.
- Tuberous roots, like dahlias, should be cut apart with a sharp knife. Every division must have a piece of the original stem and a growth bud attached. After division they can either be replanted or stored for spring planting.
Remember that perennials, like armies, move on their bellies. They need to be fed, but not too much. Transplant shock can be minimized with a judicious feeding of nitrogen – but take care not to burn tender roots. More fertilizer can be added 6 to 8 weeks after transplanting. And, watch diseased plants. If you’ve got an infected perennial that’s just hanging on, don’t spread the problem around. Make sure you’re working with healthy plants that you like and select a spot where you think they’ll do well.
If you want to learn more about transplanting and gardening in general, visit The California Master Gardener Program online. The garden experts have designed the California Garden Web to serve as a portal to organize and extend the University of California’s vast collection of research-based information about gardening to the public. The user-friendly site focuses on sustainable gardening practices and uses a question- and-answer format to present practical solutions. Click on the link to go to The California Garden Website.
|Image: Pamela Geisel, Academic Coordinator Statewide Master Gardener Program|